Multifunctional mechanical metamaterial structure cell element capable of realizing indifferent balance and zero force state and metamaterial structure

Abstract

The invention relates to the technical field of metamaterials, and discloses a multifunctional mechanical metamaterial structure cell element and metamaterial structure capable of realizing indifferent balance and zero force state, and the metamaterial structure cell element comprises a neutral and stable tensegrity structure and a control unit which are coupled; the tensegrity structure provides indifferent balance and zero force state characteristics; when the tensegrity structure deforms to a set threshold value, the control unit autonomously abandons or keeps the neutral stability condition of the tensegrity structure, and switching between the elastic body and neutral stability is achieved. The metamaterial structure comprises a plurality of metamaterial structure cell elements, the metamaterial structure cell elements are arranged in an array mode, and every two adjacent metamaterial structure cell elements are connected through the tail ends of straight rods or supporting rods. The method has the beneficial effects that the properties similar to ideal rigidity and plasticity, mechanism and liquid can be shown at a certain stage of deformation, and the method can play a role in scenes such as wave regulation and control, shape adaptation and maintenance and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of metamaterials, and specifically to a multifunctional mechanical metamaterial structural cell and a metamaterial structure that can achieve neutral equilibrium and zero-force state. Background Art

[0002] In the process of the development of human society, the level of productivity is closely related to the level of people's understanding and utilization of materials. Since the 20th century, with the progress of science and technology, natural materials and traditional manufacturing and processing technologies have gradually been unable to meet people's demands for stronger, richer, and more intelligent material properties in aspects such as architecture, automobiles, electronics, bioengineering, and aerospace. By reasonably designing the microstructure of traditional materials to achieve unique and strange unconventional mechanical properties, mechanical metamaterials have emerged as the times require.

[0003] Although the specific mechanical behaviors of mechanical metamaterials such as negative Poisson's ratio, rigid-flexible coupling, light weight, high strength and toughness, negative compressibility, and isotropy have broken many inherent cognitions about materials, the boundaries between elasticity and plasticity, elastic bodies and mechanisms, and solids and liquids still exist. In recent years, many researchers have tried to break this boundary to further improve and explore the performance and design space of materials.

[0004] In the field of flexible metamaterial design, since most of its deformations are based on the elastic connection of modules such as origami, a zero-deformation mode appears. This deformation mode consumes very little or no elastic energy and plays a key role in realizing reconfigurable elastic characteristics. For example, researchers have proposed a 3D metamaterial with engineering zero modes, which can achieve tunable harmonic manipulation in 1D, 2D, and 3D systems by reversibly switching between all 7 extreme modes from the zero mode (solid state) to the six-mode (near-gaseous state). Similar to the zero-deformation mode, some researchers are more concerned with the unloading characteristics of the structure similar to plasticity, that is, neutral equilibrium. By using a neutrally stable single-degree-of-freedom self-stress articulated structure unit cell as a building block to create a deformable structural material, all deformation motions are energy-equivalent, thus not generating a force response. However, different from a motion mechanism, by making the articulated part transform between solid and liquid, or through the active control of sensors and motors, a rapid and controllable conversion of elastoplastic mechanical properties can be achieved.

[0005] Although the current structural design of mechanical metamaterials can already achieve certain ideal elastoplastic, mechanism, and liquid characteristics in elastic bodies, the boundaries between them still exist. We need to perform operations such as restructuring, phase change, and active control on the materials to achieve the neutral equilibrium and zero-force state characteristics in different directions or states, and it cannot show multiple deformation modes during a continuous deformation to truly combine the properties of elastic bodies with ideal elastoplasticity, mechanisms, and liquids. Summary of the Invention

[0006] To address the deficiencies in the prior art, the present invention provides a multifunctional mechanical metamaterial structure capable of achieving indifferent equilibrium and zero-force state, which is composed of a neutrally stable tensegrity structure coupled with a control unit. The neutrally stable tensegrity structure provides the characteristics of indifferent equilibrium and zero-force state, enabling it to exhibit properties similar to ideal rigid-plastic, mechanism, and liquid at a certain stage of deformation, and can play a role in scenarios such as wave regulation, shape adaptation, and maintenance.

[0007] To achieve the above object, the present invention is realized through the following technical solutions:

[0008] According to one aspect of the present invention, there is provided a multifunctional mechanical metamaterial structure cell capable of achieving indifferent equilibrium and zero-force state, including a neutrally stable tensegrity structure and a control unit coupled thereto; the tensegrity structure provides the characteristics of indifferent equilibrium and zero-force state; when the tensegrity structure deforms to a set threshold, the control unit autonomously abandons or maintains the neutrally stable condition of the tensegrity structure, realizing the switch between elastomer and neutrally stable state.

[0009] Further, the tensegrity structure includes a first straight rod, a second straight rod, and a support rod connected by a first hinge center. The angle between the first straight rod and the second straight rod is 180 degrees. The support rod is located between the first straight rod and the second straight rod. A first elastomer is provided between the end of the first straight rod and the end of the support rod, and a second elastomer is provided between the end of the second straight rod and the end of the support rod.

[0010] Further, the control unit is a combination structure of a non-elastic rope and a pre-tensioned spring, and this combination structure is located between the end of the first straight rod and the first hinge center.

[0011] Further, or the control unit is two constraint structures and a third elastomer connected by a second hinge center. The ends of the two constraint structures are respectively connected to the end of the first straight rod and the end of the support rod; the end of the third elastomer is connected to the first hinge center.

[0012] Further, the constraint structure is a constraint rod.

[0013] According to another aspect of the present invention, there is provided a multifunctional mechanical metamaterial structure capable of achieving indifferent equilibrium and zero-force state, including a plurality of metamaterial structure cells. The plurality of metamaterial structure cells are arranged in an array, and adjacent two metamaterial structure cells are connected by the ends of straight rods or support rods.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1. The present invention is composed of a neutrally stable tensegrity structure coupled with a control unit. The neutrally stable tensegrity structure provides the characteristics of indifferent equilibrium and zero-force state, enabling it to exhibit properties similar to ideal rigid-plastic, mechanism, and liquid at a certain stage of deformation, and can play a role in scenarios such as wave regulation, shape adaptation, and retention.

[0016] 2. When the structure deforms to a set threshold, the control unit actively abandons or maintains the neutrally stable condition of the tensegrity structure, realizing the automatic switching between the elastomer and neutral stability. This enables the material to possess a certain degree of intelligence while having conventional mechanical properties such as load-bearing and energy absorption, and can better meet the complex and changing engineering application requirements. This solution truly combines the characteristics of elastomers and ideal rigid-plastic, mechanism, and liquid, breaking their boundaries and enabling the material to autonomously switch between these characteristics during continuous deformation without relying on reconstruction, phase change, or active control.

[0017] 3. The present invention has potential application values in the fields of intelligent perception, self-regulation, mechanical exoskeletons, wave regulation, vibration isolation, energy absorption, and inverse design of nonlinear behaviors, and is conducive to deepening and expanding the understanding of the mechanical behaviors of materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG Figure 1 is a schematic diagram of a multifunctional mechanical metamaterial structural cell that can achieve indifferent equilibrium and zero-force state of the present invention; Figure 1 ;

[0019] FIG Figure 2 is a schematic diagram of a multifunctional mechanical metamaterial structural cell that can achieve indifferent equilibrium and zero-force state of the present invention; Figure 2 ;

[0020] FIG Figure 3 is a schematic diagram of a metamaterial array structure composed of metamaterial structural cells where the energy of the same elastic segment state is lower than the energy of the indifferent equilibrium state shown in Example 1;

[0021] FIG Figure 4 is a force diagram of Example 1;

[0022] FIG Figure 5 is a stress-strain relationship diagram of Example 1;

[0023] FIG Figure 6 is a schematic diagram of a metamaterial array composed of metamaterial structural cells with different energy levels and switching direction sequences in Example 2;

[0024] FIG Figure 7 is a stress-strain relationship diagram of Example 2;

[0025] FIG Figure 8 is a force diagram and a stress-strain relationship diagram of Example 3;

[0026] Reference numerals shown in the drawings: 1. First hinge center; 2. First straight rod; 3. Second straight rod; 4. Support rod; 5. First elastic body; 6. Second elastic body; 7. Inelastic rope; 8. Pre-tensioned spring; 9. Second hinge center; 10. Constraint structure; 11. Third elastic body; Detailed implementation manners

[0027] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by this application.

[0028] The present invention proposes a design scheme of a multifunctional mechanical metamaterial that can achieve neutral equilibrium and zero-force state. The designed structure is composed of a neutrally stable tensegrity structure coupled with a control unit. The neutrally stable tensegrity structure provides the characteristics of neutral equilibrium and zero-force state, enabling it to exhibit properties similar to ideal rigid-plastic, mechanism, and liquid at a certain stage of deformation, and can play a role in scenarios such as wave regulation, shape adaptation, and maintenance. When the structure deforms to a set threshold, the control unit autonomously abandons or maintains the neutrally stable condition of the tensegrity structure, realizing the switch between the elastic body and neutral stability, so that the material has certain intelligence while having conventional mechanical properties such as load-bearing and energy absorption, and can better meet the complex and changeable engineering application requirements.

[0029] This scheme truly combines the characteristics of elastic bodies and ideal rigid-plastic, mechanism, and liquid, breaks their boundaries, enables the material to autonomously switch between these characteristics during continuous deformation, and does not rely on reconstruction, phase change, or active control. By designing the metamaterial structure, the threshold and direction of the change in deformation behavior can be precisely preset to achieve continuous and autonomous free switching between the elastic body and neutral equilibrium and zero-force state. The behavior of this structure in the elastic section has strong designability, can achieve excellent linear elasticity and negative stiffness characteristics under quasi-static loading, and at the same time has an arrayable spatial characteristic, can achieve any Poisson's ratio and Gaussian curvature, and has extremely strong shape designability. Different array methods can make the material exhibit different specific mechanical properties, such as multi-energy platform characteristics, stress-strain behavior changing with loading, etc., and can be applied in multiple different scenarios, and have potential application value in the fields of intelligent sensing, self-regulation, mechanical exoskeletons, wave regulation, vibration isolation, energy absorption, and reverse design of non-linear behavior, and are conducive to deepening and expanding the understanding and comprehension of the mechanical behavior of materials. The specific structure of the metamaterial structure unit cell is as follows:

[0030] As Figure 1-2As shown, a multifunctional mechanical metamaterial structural cell capable of achieving indifferent equilibrium and zero-force state is disclosed, including a neutrally stable tensegrity structure and a control unit coupled thereto; the tensegrity structure provides the characteristics of indifferent equilibrium and zero-force state; when the tensegrity structure deforms to a set threshold, the control unit autonomously abandons or maintains the neutrally stable condition of the tensegrity structure, realizing the switching between the elastomer and neutral stability.

[0031] Specifically, as Figure 1 shown, one structure of the metamaterial structural cell is disclosed. The tensegrity structure includes a first straight rod 2, a second straight rod 3, and a support rod 4 connected through a first hinge center 1. The angle between the first straight rod 2 and the second straight rod 3 is 180 degrees. The support rod 4 is located between the first straight rod 2 and the second straight rod 3. A first elastomer 5 is provided between the end of the first straight rod 2 and the end of the support rod 4, and a second elastomer 6 is provided between the end of the second straight rod 3 and the end of the support rod 4. The control unit is a combined structure of a non-elastic rope 7 and a pre-tensioned spring 8, and this combined structure is located between the end of the first straight rod 2 and the first hinge center 1. The metamaterial structural cell can achieve different mechanical properties, state switching thresholds, and directions of the elastic segments, as Figure 1 shown. In the neutrally stable tensegrity structure and the control unit, the material parameters k 1 、k 2 determine the mechanical properties of the elastic segment; the above material parameters and the geometric parameters l 0 、l 2 together determine the state switching threshold; as the structure deforms, the geometric parameter θ changes accordingly, and together with the threshold, it determines the current deformation mode. According to the different loading directions, the direction and order of state switching also change.

[0032] As Figure 2 shown, another structure of the metamaterial structural cell is disclosed. The tensegrity structure is the same as Figure 1 the above, and the control unit is composed of two constraint structures 10 and a third elastomer 11 connected through a second hinge center 9. The ends of the two constraint structures 10 are respectively connected to the end of the first straight rod 2 and the end of the support rod 4; the end of the third elastomer 11 is connected to the first hinge center 1. In this structure, the energy of its elastic segment is relatively high with respect to the indifferent equilibrium and zero-force state. The combination of the two can meet the mechanical property requirements of different scenarios.

[0033] A multifunctional mechanical metamaterial structure capable of achieving indifferent equilibrium and zero-force state includes a plurality of metamaterial structural cells. The plurality of metamaterial structural cells are arranged in an array, and adjacent two metamaterial structural cells are connected through the ends of a straight rod or the support rod 4. The array structure can be set as needed, and specific details can be seen in the embodiments.

[0034] Embodiment 1:

[0035] Figures 3-5 The following shows a preferred embodiment of the present invention, which is a metamaterial array composed of metamaterial structural unit cells where the energy of the same elastic segment state is lower than that of the indifferent equilibrium state. When the structure deforms, it first experiences an elastic segment with negative stiffness. If unloaded in this state, the structure will return to its initial state; after reaching the threshold, it enters the indifferent equilibrium and zero-force state, where the force response is zero. If unloaded in this state, the structure will maintain its current state. If loaded from the vertical direction, the switching order changes, and the elastic segment structure will actively conform to the deformation, similar to the negative force stage of bistability. The elastic segment state can meet conventional scenarios such as load-bearing and energy absorption, and the indifferent equilibrium state after reaching the threshold can well adapt to certain special scenarios and tasks, such as wave regulation and shape compliant adaptation.

[0036] Embodiment 2:

[0037] Figures 6-7 The following shows another preferred embodiment of the present invention, which is a metamaterial array composed of metamaterial structural unit cells with different energy levels and switching direction orders. When the structure deforms, it experiences the elastic segment and the indifferent equilibrium and zero-force state in a specific order, which can well meet the requirements of complex tasks for force response, such as being used to assist exoskeletons. It provides support for specific actions within a specific range and does not cause obstruction or influence during other specific activities, which often relies on active control in current research. At the same time, existing research has proven that tensegrity structures can achieve arbitrary Gaussian curvature and Poisson's ratio, and the loading (strain) direction of the metamaterial array can also be customized as needed, with extremely strong practicality and designability.

[0038] Embodiment 3:

[0039] As Figure 8Another preferred embodiment of the present invention is shown. It is two metamaterial arrays composed of metamaterial structural cells with different elastic segment energies lower than the energy of the indifferent equilibrium state, and the switching thresholds increase or decrease sequentially from the inside to the outside. For the array method with increasing stiffness, when the structure deforms, multiple elastic segments and indifferent equilibrium segments will appear alternately in sequence, and the energy curve exhibits a stepped platform characteristic, and all elastic segments have negative stiffness, which is of great significance for the energy absorption and impact protection of reusable multi-segment low-rebound. For the array method with decreasing stiffness, when the structure deforms, according to the current load condition, the metamaterial cells in different inner sections will be activated to perform force response, so as to achieve a force-deformation response related to the load, which has a strong analogy with viscous fluid (the force response is related to the shear strain rate). According to existing research, this adjustable stiffness usually requires external active control, such as phase change, etc., and usually manifests in different stages of deformation, and cannot be changed according to the load, lacking intelligence. In addition to being able to autonomously adjust the deformation behavior according to the load, this structure can also quickly judge the current load according to the deformation situation, possessing a certain degree of intelligent characteristics.

Claims

1. A multifunctional mechanical metamaterial structural cell capable of achieving random balance and zero-force state, characterized in that: It comprises a coupled neutrally stable tensegrity structure and a control unit; the tensegrity structure provides random equilibrium and zero-force state characteristics; when the tensegrity structure is deformed to a set threshold, the control unit autonomously abandons or maintains the neutral stability condition of the tensegrity structure to achieve switching between the elastic body and the neutral stability.

2. The multifunctional mechanical metamaterial structure cell capable of achieving random balance and zero-force state according to claim 1, characterized in that: The tensegrity structure comprises a first straight rod (2), a second straight rod (3) and a support rod (4) connected via a first hinge center (1); the angle between the first straight rod (2) and the second straight rod (3) is 180 degrees; the support rod (4) is located between the first straight rod (2) and the second straight rod (3); a first elastic body (5) is arranged between the end of the first straight rod (2) and the end of the support rod (4); and a second elastic body (6) is arranged between the end of the second straight rod (3) and the end of the support rod (4).

3. A multifunctional mechanical metamaterial structure cell capable of achieving random balance and zero-force state according to claim 1 or 2, characterized in that: The control unit is a combination structure of a non-elastic rope (7) and a pre-tensioned spring (8), and the combination structure is located between the end of the first straight rod (2) and the first hinge center (1).

4. A multifunctional mechanical metamaterial structure cell capable of achieving random balance and zero-force state according to claim 1 or 2, characterized in that: The control unit comprises two constraint structures (10) and a third elastic body (11) connected by a second hinge center (9); the ends of the two constraint structures (10) are respectively connected to the ends of the first straight rod (2) and the support rod (4); and the end of the third elastic body (11) is connected to the first hinge center (1).

5. The multifunctional mechanical metamaterial structure cell capable of achieving random balance and zero-force state according to claim 4, characterized in that: The restraining structure (10) is a restraining rod.

6. A multifunctional mechanical metamaterial structure capable of achieving random balance and zero-force state, characterized in that: It comprises a plurality of metamaterial structure cells, the plurality of metamaterial structure cells are arranged in an array, and two adjacent metamaterial structure cells are connected via the ends of a straight rod or a support rod (4).

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